Apparatus and method for controlling intake air amount of internal combustion engine

ABSTRACT

In an internal combustion engine provided with a variable valve mechanism that varies at least a valve operating characteristic (valve lift amount, valve operating angle and the like) of an intake valve, a target volume flow ratio equivalent to a target torque of the engine is obtained to be converted into a valve opening area, and a target valve operating characteristic of the variable valve mechanism is set based on the converted valve opening area, to control the variable valve mechanism so that an actual valve operating characteristic reaches a target valve operating angle, thereby executing with high accuracy an intake air amount control mainly by the variable valve mechanism.

FIELD OF THE INVENTION

[0001] The present invention relates to a technique for controlling anintake air amount by a variable valve mechanism in an engine, whichvaries at least an operation characteristic of an intake valve.

RELATED ART OF THE INVENTION

[0002] Heretofore, there has been known a variable valve mechanismconstituted to successively vary a valve lift amount and a valveoperating angle (refer to Japanese Unexamined Patent Publication2001-012262).

[0003] In an engine provided with such a variable valve mechanism, avalve lift amount and a valve operating angle are controlled by thevariable valve mechanism, to control an intake air amount independentlyof a throttle valve. However, in this case, since a torque control bythe throttle valve cannot be performed, there occurs a problem of howthe torque linearity is ensured.

[0004] Further, in the case where the intake air amount control isperformed by the above variable valve mechanism, it is impossible togenerate, in an intake air passage, a negative pressure for the canisterpurging or the blowby gas processing. Moreover, from such a mechanism,since there is a limitation in controllable valve operatingcharacteristic (valve lift amount and valve operating angle), it becomesnecessary to perform a control by the throttle valve in addition to thecontrol by the variable valve mechanism, depending on conditions.

[0005] In such a case, there occurs a problem of how the cooperativecontrol of the variable valve mechanism and the throttle valve isperformed (how the control accuracy is ensured).

[0006] On the other hand, there has been known an engine having aconstitution wherein a target torque is set based on an acceleratorangle and an engine rotation speed, and an operating characteristic ofintake valve and/or an opening of throttle valve are changed so that anintake air amount corresponding to the target torque can be obtained(refer to Japanese Unexamined Patent Publication No. 6-272580). In thisengine, operation timing of intake valve is obtained based on the targettorque and the engine rotation speed, so as to enable to change thegenerated torque linearly corresponding to the throttle valve opening.

[0007] However, such a conventional mechanism relates to a variablevalve timing mechanism (apparatus) that varies “operation timing” ofintake valve, and is to control the intake air amount mainly by thethrottle valve. Therefore, it cannot be applied to an engine in whichthe intake air amount is controlled mainly by the variable valvemechanism. The above problem still remains unsolved.

SUMMARY OF THE INVENTION

[0008] The present invention has been achieved in view of the aboveproblems and has an object to ensure torque linearity with high accuracywhen performing an intake air amount control by a variable valvemechanism.

[0009] A further object of the present invention is to appropriatelyperform a cooperative control of the variable valve mechanism and athrottle valve so as to enable to cope with the generation of requestednegative pressure and the like, while executing the intake air amountcontrol (torque control) mainly by the variable valve mechanism.

[0010] In order to achieve the above objects, according to the intakeair amount control of the present invention, in an engine provided witha variable valve mechanism that varies at least a valve operatingcharacteristic of an intake valve, a target intake air amount equivalentto a target torque is set in accordance with operating conditions of theengine, a target valve operating characteristic is set based on the settarget intake air amount, and the variable valve mechanism is controlledso that an actual valve operating characteristic reaches the targetvalve operating characteristic.

[0011] With such a constitution, the intake air amount control mainly bythe variable valve mechanism can be executed with high accuracy, whileensuring the torque linearity.

[0012] Further, in an engine provided with a throttle valve driven toopen and close by an actuator in addition to the above variable valvemechanism, the variable valve mechanism is controlled so that the actualvalve operating characteristic becomes the target valve operatingcharacteristic, and also a target throttle opening of the throttle valveis set based on the target intake air amount and the valve operatingcharacteristic to control the actuator so that an actual throttleopening reaches the target throttle opening.

[0013] With such a constitution, the intake air amount control mainly bythe variable valve mechanism and also with the variable valve mechanismcooperated with the throttle valve can be executed. Thus, it becomespossible to execute the intake air amount control with higher accuracyand also to cope with the negative pressure request and the like.

[0014] The other objects and features of this invention will becomeunderstood from the following description with accompanying drawings.

BRIEF EXPLANATION OF THE DRAWINGS

[0015]FIG. 1 is a view showing a system structure of an internalcombustion engine in an embodiment of the present invention.

[0016]FIG. 2 is a cross section view showing a variable valve mechanismin the embodiment (A-A cross section view of FIG. 3)

[0017]FIG. 3 is a side elevation view of the variable valve mechanism.

[0018]FIG. 4 is a top plan view of the variable valve mechanism.

[0019]FIG. 5 is a perspective view showing an eccentric cam for use inthe variable valve mechanism.

[0020]FIG. 6A and FIG. 6B are cross section views showing an operationof the variable valve mechanism at a low lift condition (B-B crosssection view of FIG. 3).

[0021]FIG. 7A and FIG. 7B are cross section views showing an operationof the variable valve mechanism at a high lift condition (B-B crosssection view of FIG. 3).

[0022]FIG. 8 is a valve lift characteristic diagram corresponding to abase end face and a cam surface of a swing cam in the variable valvemechanism.

[0023]FIG. 9 is a characteristic diagram showing valve timing and valvelift of the variable valve mechanism.

[0024]FIG. 10 is a perspective view showing a rotational drivingmechanism of a control shaft in the variable valve mechanism.

[0025]FIG. 11 is a longitudinal section view of a variable valve timingmechanism in the embodiment.

[0026]FIG. 12 is an entire block diagram showing an intake air amountcontrol (torque control) in the embodiment.

[0027]FIG. 13 to FIG. 20 are block diagrams showing the details ofintake air amount control in the embodiment, in which:

[0028]FIG. 13 is a block diagram showing the setting of a target phaseangle of the variable valve timing mechanism;

[0029]FIG. 14A and FIG. 14B are a block diagram showing the setting of atarget operating angle of the variable valve mechanism;

[0030]FIG. 15 is a block diagram showing the correction by a flow lossvalue in accordance with a valve operating characteristic (a liftamount);

[0031]FIG. 16 is a block diagram showing the calculation of a valvetiming based correction value KHOSIVC for the correction in accordancewith closing timing of an intake valve;

[0032]FIG. 17 is a block diagram showing the setting of a valve upstreampressure based correction value KMANIP for the correction in accordancewith an intake pressure on the upstream side of intake valve;

[0033]FIG. 18 is a block diagram showing the setting of a targetthrottle opening of a throttle valve;

[0034]FIG. 19 is a block diagram showing the calculation of an intakevalve opening based correction value KAVEL for the correction inaccordance with an actual operating characteristic of intake valve; and

[0035]FIG. 20 is a block diagram showing the calculation of a ratioWQH0VEL of volume flow passed through the intake valve at the time whenthe throttle valve is fully opened and a ratio RQH0VEL of volume flowactually passed through the intake valve.

[0036]FIG. 21 to FIG. 24 are block diagrams showing the details ofintake air amount control in another embodiment, in which:

[0037]FIG. 21 is a block diagram showing the setting of a targetoperating angle of the variable valve mechanism and a target phase angleof the variable valve timing mechanism;

[0038]FIG. 22 is a block diagram showing the calculation of an effectiveopening area of the intake valve;

[0039]FIG. 23 is a block diagram showing a volume flow ratio of theintake valve; and

[0040]FIG. 24 is a block diagram showing the setting of a targetthrottle opening of the throttle valve.

[0041]FIG. 25 is a diagram showing a lift characteristic of the intakevalve.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] Embodiments of the present invention will be described based onthe drawings.

[0043]FIG. 1 is a structural diagram of an internal combustion enginefor vehicle. In FIG. 1, in an intake passage 102 of an internalcombustion engine 101, an electronically controlled throttle 104 isdisposed for driving a throttle valve 103 b to open and close by athrottle motor 103 a. Air is sucked into a combustion chamber 106 viaelectronically controlled throttle 104 and an intake valve 105.

[0044] A combusted exhaust gas is discharged from combustion chamber 106via an exhaust valve 107, purified by an exhaust purification catalyst108, and then emitted into the atmosphere via a muffler 109.

[0045] Exhaust valve 107 is driven by a cam 111 axially supported by anexhaust side camshaft 110, while keeping a valve lift amount and a valveoperating angle thereof constant. On the contrary, the valve lift amountand valve operating angle of intake valve 105 are successively varied bya variable valve mechanism (VEL) 112, and valve timing thereof issuccessively varied by a variable valve timing mechanism (VTC) 113.Further, there may be provided a mechanism for varying valve operatingcharacteristics of intake valve 105 and exhaust valve 107.

[0046] A control unit (C/U) 114 incorporating therein a microcomputer,controls the drive of electronically controlled throttle 104, variablevalve mechanism (VEL) 112 and variable valve timing mechanism (VTC) 113in accordance with an accelerator opening APO to be detected by anaccelerator opening sensor APS 116, so that an intake air amountcorresponding to the accelerator opening can be obtained based on anopening of throttle valve 103 b and an opening characteristic of intakevalve 105.

[0047] Specifically, the opening of throttle valve 103 b is controlledso as to generate a constant negative pressure (target Boost) for thecanister purging and the blowby gas processing, while controlling theintake air amount by controlling the valve lift amount (and valveoperating angle) of variable valve mechanism (VEL) 112.

[0048] Note, under an operating condition where there is no negativepressure request, a so-called throttle-less control in which throttlevalve 103 b is kept full-opened and the intake air amount is controlledonly by variable valve mechanism (VEL) 112, is performed. In the casewhere the intake air amount cannot be controlled only by variable valvemechanism (VEL) 112, throttle valve 103 b is also controlled.

[0049] Control unit (C/U) 114 receives various detection signals from anair flow meter 115 detecting an intake air amount (mass flow) Qa, acrank angle sensor 117 taking out a rotation signal from a crankshaft, athrottle sensor 118 detecting an opening TVO of throttle valve 103 b, awater temperature sensor 119 detecting a cooling water temperature Tw ofengine 101 and the like, in addition to a detection signal fromaccelerator opening sensor APS 116.

[0050] In control unit (C/U) 114, an engine rotation speed Ne iscalculated based on the rotation signal output from crank angle sensor117. Further, an electromagnetic fuel injection valve 131 is disposed onan intake port 130 on the upstream side of intake valve 105 of eachcylinder. Fuel injection valve 131 injects fuel adjusted at apredetermined pressure toward intake valve 105 when driven to open by aninjection pulse signal from control unit (C/U) 114.

[0051] Here, a structure of variable valve mechanism (VEL) 112 will bedescribed.

[0052]FIG. 2 to FIG. 4 show in detail the structure of variable valvemechanism (VEL) 112 (however, this merely shows one example, and thepresent invention is not limited to such a structure).

[0053] Variable valve mechanism (VEL) 112 shown in FIG. 2 to FIG. 4includes a pair of intake valves 105, 105, a hollow camshaft (driveshaft) 13 rotatably supported by a cam bearing 14 of a cylinder head 11,two eccentric cams (drive cams) 15, 15 being rotation cams axiallysupported by a camshaft 13, a control shaft 16 rotatably supported bythe same cam bearing 14 at an upper position of camshaft 13, a pair ofrocker arms 18, 18 swingingly supported by control shaft 16 through acontrol cam 17, and a pair of independent swing cams 20, 20 disposed toupper end portions of intake valves 105, 105 through valve lifters 19,19, respectively.

[0054] Eccentric cams 15, 15 are connected with rocker arms 18, 18 bylink arms 25, 25, respectively. Rocker arms 18, 18 are connected withswing cams 20, 20 by link members 26, 26. Rocker arms 18, 18, link arms25, 25, and link members 26, 26 constitute a transmission mechanism.

[0055] Each eccentric cam 15, as shown in FIG. 5, is formed in asubstantially ring shape and includes a cam body 15 a of small diameter,a flange portion 15 b integrally formed on an outer surface of cam body15 a. A camshaft insertion hole 15 c is formed through the interior ofeccentric cam in an axial direction, and also a center axis X of cambody 15 a is biased from a center axis Y of camshaft 13 by apredetermined amount.

[0056] Eccentric cams 15, 15 are pressed and fixed to both outer sidesof camshaft 13 via camshaft insertion holes 15 c at positions notinterfering with valve lifters 19, 19. Outer peripheral surfaces 15 d,15 d of cam bodies 15 a, 15 a are formed in the same profile.

[0057] Each rocker arm 18, as shown in FIG. 4, is bent and formed in asubstantially crank shape, and a central base portion 18 a thereof isrotatably supported by control cam 17.

[0058] A pin hole 18 d is formed through one end portion 18 b which isformed to protrude from an outer end portion of base portion 18 a. A pin21 to be connected with a tip portion of link arm 25 is pressed into pinhole 18 d. A pin hole 18 e is formed through the other end portion 18 cwhich is formed to protrude from an inner end portion of base portion 18a. A pin 28 to be connected with one end portion 26 a (to be describedlater) of each link member 26 is pressed into pin hole 18 e.

[0059] Control cam 17 is formed in a cylindrical shape and fixed to aperiphery of control shaft 16. As shown in FIG. 2, a center axis P1position of control cam 17 is biased from a center axis P2 position ofcontrol shaft 16 by α.

[0060] Swing cam 20 is formed in a substantially lateral U-shape asshown in FIG. 2, FIG. 6 and FIG. 7, and a supporting hole 22 a is formedthrough a substantially ring-shaped base end portion 22. Camshaft 13 isinserted into base end portion 22 to be rotatably supported. Also, a pinhole 23 a is formed through an end portion 23 positioned at the otherend portion 18 c of rocker arm 18.

[0061] A base circular surface 24 a of base end portion 22 side and acam surface 24 b extending in an arc shape from base circular surface 24a to an edge of end portion 23, are formed on a bottom surface of swingcam 20. Base circular surface 24 a and cam surface 24 b are in contactwith a predetermined position of an upper surface of each valve lifter19 corresponding to a swing position of swing cam 20.

[0062] Namely, according to a valve lift characteristic shown in FIG. 8,as shown in FIG. 2, a predetermined angle range θ1 of base circularsurface 24 a is a base circle interval and a range of from base circleinterval θ1 of cam surface 24 b to a predetermined angle range θ2 is aso-called ramp interval, and a range of from ramp interval θ2 of camsurface 24 b to a predetermined angle range θ3 is a lift interval.

[0063] Link arm 25 includes a ring-shaped base portion 25 a and aprotrusion end 25 b protrudingly formed on a predetermined position ofan outer surface of base portion 25 a. A fitting hole 25 c rotatably tobe fitted with the outer surface of cam body 15 a of eccentric cam 15 isformed on a central position of base portion 25 a. Also, a pin hole 25 binto which pin 21 is rotatably inserted is formed through protrusion end25 b.

[0064] Link member 26 is formed in a linear shape of predeterminedlength and pin insertion holes 26 c, 26 d are formed through bothcircular end portions 26 a, 26 b. End portions of pins 28, 29 pressedinto pin hole 18 d of the other end portion 18 c of rocker arm 18 andpin hole 23 a of end portion 23 of swing cam 20, respectively, arerotatably inserted into pin insertion holes 26 c, 26 d. Snap rings 30,31, 32 restricting axial transfer of link arm 25 and link member 26 aredisposed on respective end portions of pins 21, 28, 29.

[0065] In such a constitution, depending on a positional relationbetween the center axis P2 of control shaft 16 and the center axis P1 ofcontrol cam 17, as shown in FIG. 6 and FIG. 7, it is possible to varythe valve lift amount, and by driving control shaft 16 to rotate, theposition of the center axis P2 of control shaft 16 relative to thecenter axis P1 of control cam 17 is changed.

[0066] Control shaft 16 is driven to rotate within a predetermined anglerange by a DC servo motor (actuator) 121 disposed at one end portionthereof. By varying the operating angle of control shaft 16 by DC servomotor 121, the valve lift amount and valve operating angle of each ofintake valves 105, 105 are successively varied (refer to FIG. 9).

[0067] In FIG. 10, DC servo motor 121 is arranged so that the rotationshaft thereof is parallel with control shaft 16, and a bevel gear 122 isaxially supported by the tip portion of the rotation shaft.

[0068] On the other hand, a pair of stays 123 a, 123 b are fixed to thetip portion of control shaft 16. A nut 124 is swingingly supportedaround an axis parallel to control shaft 16 connecting the tip portionsof the pair of stays 123 a, 123 b.

[0069] A bevel gear 126 meshed with bevel gear 122 is axially supportedat the tip portion of a threaded rod 125 engaged with nut 124. Threadedrod 126 is rotated by the rotation of DC servo motor 121, and theposition of nut 124 engaged with threaded rod 125 is displaced in theaxial direction of threaded rod 125, so that control shaft 16 isrotated.

[0070] Here, the valve lift amount is decreased as the position of nut124 approaches bevel gear 126, while the valve lift amount is increasedas the position of nut 124 gets away from bevel gear 126.

[0071] Further, a potentiometer type operating angle sensor 127detecting the operating angle of control shaft 16 is disposed on the tipportion of control shaft 16, as shown in FIG. 10. Control unit 114feedback controls DC servo motor (actuator) 121 so that an actualoperating angle detected by operating angle sensor 127 coincides with atarget operating angle.

[0072] Next, the structure of variable valve timing mechanism (VTC) 113will be described. FIG. 11 shows in detail the structure of variablevalve timing mechanism (VTC) 113. (However, this structure is merely oneexample, and the present invention is not limited to such a structure).Variable valve timing mechanism (VTC) 113 shown in FIG. 11 is aso-called vane type variable valve timing mechanism, and comprises: acam sprocket 51 (timing sprocket) which is rotatably driven by acrankshaft 120 via a timing chain; a rotation member 53 secured to anend portion of intake side camshaft 13 and rotatably housed inside camsprocket 51; a hydraulic circuit 54 that relatively rotates rotationmember 53 with respect to cam sprocket 51; and a lock mechanism 60 thatselectively locks a relative rotation position between cam sprocket 51and rotation member 53 at predetermined positions.

[0073] Cam sprocket 51 comprises: a rotation portion (not shown in thefigure) having on an outer periphery thereof, teeth for engaging withtiming chain (or timing belt); a housing 56 located forward of therotation portion, for rotatably housing rotation member 53; and a frontcover and a rear cover (not shown in the figure) for closing the frontand rear openings of housing 56.

[0074] Housing 56 presents a cylindrical shape formed with both frontand rear ends open and with four partition portions 63 protrudinglyprovided at positions on the inner peripheral face at 90° in thecircumferential direction, four partition portions 63 presenting atrapezoidal shape in transverse section and being respectively providedalong the axial direction of housing 56.

[0075] Rotation member 53 is secured to the front end portion of intakeside camshaft 13 and comprises an annular base portion 77 having fourvanes 78 a, 78 b, 78 c, and 78 d provided on an outer peripheral face ofbase portion 77 at 90° in the circumferential direction.

[0076] First through fourth vanes 78 a to 78 d present respectivecross-sections of approximate trapezoidal shapes. The vanes are disposedin recess portions between each partition portion 63 so as to formspaces in the recess portions to the front and rear in the rotationdirection. Advance angle side hydraulic chambers 82 and retarded angleside hydraulic chambers 83 are thus formed.

[0077] Lock mechanism 60 has a construction such that a lock pin 84 isinserted into an engagement hole (not shown in the figure) at a rotationposition (in the reference operating condition) on the maximum retardedangle side of rotation member 53.

[0078] Hydraulic circuit 54 has a dual system oil pressure passage,namely a first oil pressure passage 91 for supplying and discharging oilpressure with respect to advance angle side hydraulic chambers 82, and asecond oil pressure passage 92 for supplying and discharging oilpressure with respect to retarded angle side hydraulic chambers 83. Tothese two oil pressure passages 91 and 92 are connected a supply passage93 and drain passages 94 a and 94 b, respectively, via anelectromagnetic switching valve 95 for switching the passages.

[0079] An engine driven oil pump 97 for pumping oil in an oil pan 96 isprovided in supply passage 93, and the downstream ends of drain passages94 a and 94 b are communicated with oil pan 96.

[0080] First oil pressure passage 91 is formed substantially radially ina base 77 of rotation member 53, and connected to four branching paths91 d communicating with each advance angle side hydraulic chamber 82.Second oil pressure passage 92 is connected to four oil galleries 92 dopening to each retarded angle side hydraulic chamber 83.

[0081] With electromagnetic switching valve 95, an internal spool valveis arranged so as to control the switching between respective oilpressure passages 91 and 92, and supply passage 93 and drain passages 94a and 94 b.

[0082] Control unit (C/U) 114 controls the power supply quantity for anelectromagnetic actuator 99 that drives electromagnetic-switching valve95, based on a duty control signal superimposed with a dither signal.

[0083] For example, when a control signal of duty ratio 0% (OFF signal)is output to electromagnetic actuator 99, the hydraulic fluid pumpedfrom oil pump 47 is supplied to retarded angle side hydraulic chambers83 via second oil pressure passage 92, and the hydraulic fluid inadvance angle side hydraulic chambers 82 is discharged into oil pan 96from (first) drain passage 94 a via first oil pressure passage 91.Consequently, an inner pressure of retarded angle side hydraulicchambers 83 becomes a high pressure while an inner pressure of advanceangle side hydraulic chambers 82 becomes a low pressure, and rotationmember 53 is rotated to the most retarded angle side by means of vanes78 a to 78 d. The result of this is that the opening period (openingtiming and closing timing) of intake valve 105 is delayed.

[0084] On the other hand, when a control signal of duty ratio 100% (ONsignal) is output to electromagnetic actuator 99, the hydraulic fluidpumped from oil pump 47 is supplied to inside of advance angle sidehydraulic chambers 82 via first oil pressure passage 91, and thehydraulic fluid in retarded angle side hydraulic chambers 83 isdischarged to oil pan 96 via second oil pressure passage 92, from(second) drain passage 94 b. Therefore, retarded angle side hydraulicchambers 83 become a low pressure, and rotation member 53 is rotated tothe full to the advance angle side by means of vanes 78 a to 78 d. Dueto this, the opening period (opening timing and closing timing) of theintake valve 105 is accelerated (advanced).

[0085] In the constitution as mentioned in the above, there will bedescribed in detail an intake air amount control executed by controlunit (C/U) 114, that is a control on electronically controlled throttle104, variable valve mechanism (VEL) 112 and variable valve timingmechanism (VTC) 113 (a first embodiment).

[0086] As shown in FIG. 12, control unit (C/U) 114 includes a targetvolume flow ratio calculating section “a”, a VTC target operating anglecalculating section “b”, a VEL target operating angle calculatingsection “c” and a target throttle opening calculating section “d”.

[0087] (a) Calculation of Target Volume Flow Ratio TQH0ST

[0088] The target volume flow ratio calculating section “a” calculates atarget volume flow ratio TQH0ST equivalent to a target torque asfollows.

[0089] Firstly, a requested air amount (a requested engine air amount)Q0 corresponding to accelerator opening APO and engine rotation speed Ne(or, that so as to obtain a target torque set based on acceleratoropening APO and engine rotation speed Ne) is calculated, and also arequested ISC air amount QISC requested in an idle rotation speedcontrol (ISC) is calculated. Then, the requested engine air amount Q0 isadded with the requested ISC air amount QISC to calculate the totalrequested air amount (intake air amount) Q(=Q0+QISC). The resultanttotal requested air amount is divided by engine rotation speed Ne and adischarge amount (total cylinder volume) VOL# to calculate target volumeflow ratio TQH0ST(=Ne·VOL#).

[0090] (b) Calculation of VTC Target Phase Angle TGVT

[0091] The VTC target operating angle calculating section “b”, as shownin FIG. 13, calculates a target phase angle (TGVTC) of variable valvetiming mechanism (VTC) 113, referring to a map as shown in the figure,based on target volume flow ratio TQH0ST and engine rotation speed Ne.

[0092] Thus, control unit (C/U) 114 controls variable valve timingmechanism (VTC) 113 so that an actual VTC phase angle reaches the targetphase angle (TGVTC).

[0093] (c) Calculation of VEL Target Operating Angle TGVEL

[0094] The VEL target operating angle calculating section “c” calculatesa target operating angle TGVEL (target lift amount) of variable valvemechanism (VEL) 112 so as to ensure target volume flow ratio TQH0ST, asfollows.

[0095] First of all, target volume flow ratio TQH0ST is (inversely)transformed, to calculate a target valve opening area TVELAA. Then,based on target valve opening area TVELAA, target operating angle TGVEL(target lift amount) of control shaft 16 in variable valve mechanism(VEL) 112 is calculated.

[0096] Here, the target operating angle is set so as to increase thevalve lift amount, as target volume flow ratio TQH0ST is larger and alsoengine rotation speed Ne is higher. In the case where there is anegative pressure request, or target volume flow ratio TQH0ST cannot becontrolled by variable valve mechanism (VEL) 112, a throttle control ofthrottle valve 103 b is also performed. Note, in this embodiment, largerthe operating angle of control shaft 16 becomes, larger the lift amountof intake valve 105 becomes.

[0097] In the following, the calculation in the VEL target operatingangle calculating section “c” will be described in detail, based on FIG.14 to FIG. 16.

[0098] (c-1) Setting of Target Operating Angle TGVEL of Variable ValveMechanism (VEL) 112

[0099] In FIG. 14, at A part, target volume flow ratio TQH0ST iscompared with a minimum volume flow ratio QH0LMT, and a higher one isselected to set a volume flow ratio TQH0VEL to be realized in variablevalve mechanism (VEL) 112 (to be referred to as VEL realizing volumeflow ratio hereafter). Here, minimum volume flow ratio QH0LMT is the onerealizable (controllable) by variable valve mechanism (VEL) 112 (thatis, the volume flow ratio of when the VEL operating angle is minimum),which is calculated, in “a1” part, by retrieving a table TQH0LMT asshown in the figure, based on engine rotation speed Ne. Thus, even iftarget volume flow ratio TQH0ST is low (that is, irrespective ofoperating conditions), a target valve operating characteristic ofvariable valve mechanism (VEL) 112 can be set so that an intake airamount control by mainly by variable valve mechanism (VEL) 112 isexecuted.

[0100] When a VEL requested volume flow ratio THQ0VEL0 is less thanminimum volume flow ratio QH0LMT, this minimum volume flow ratio QH0LMTis selected. However, in such a case, target volume flow ratio TQH0STcannot be achieved only by variable valve mechanism (VEL) 112 (that is,the intake air amount control cannot be performed). Therefore, thethrottle control of throttle valve 103 b is also performed.

[0101] At B part, VEL realizing volume flow ratio TQH0VEL is convertedinto a state amount VACDNV equivalent to valve opening area (Av),VADCNV=Av·Cd/N/V (valve opening area·loss coefficient/rotationspeed/exhaust amount). Such conversion is performed as follows.

[0102] At first, an air flow amount passing through intake valve 105(that is, a cylinder intake air amount) Qc (t) (kg/sec) can berepresented by equations (1), (2) based on an equation of aone-dimensional steady flow of compressed fluid. $\begin{matrix}{{{{At}\quad {choke}\text{:}\quad \frac{Pc}{P0}} \leq \left( \frac{2}{\gamma + 1} \right)^{\frac{\gamma}{\gamma - 1}}}\quad} & \quad \\{{{{{Qc}(t)} = {\frac{{Cd} \cdot {Av} \cdot {P0}}{\sqrt{R \cdot {T0}}}\sqrt{\gamma}\left( \frac{2}{\gamma - 1} \right)^{\frac{\gamma + 1}{2{({\gamma - 1})}}}}}{{At}\quad {no}\quad {choke}\text{:}}}\quad} & (1) \\{{{Qc}(t)} = {\frac{{Cd} \cdot {Av} \cdot {P0}}{\sqrt{R \cdot {T0}}}\left( \frac{Pc}{P0} \right)^{\frac{1}{\gamma}}\sqrt{\frac{2\gamma}{\gamma - 1}\left( {1 - \left( \frac{Pc}{Pm} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}}} & (2)\end{matrix}$

[0103] In the above equations, R: a gas constant (=287) (J/(Kg·K), γ: aratio of specific heat (=1.4), Cd: an intake valve flow losscoefficient, Av: intake valve opening area (m²), P0: an intake valveupstream pressure (for example, intake manifold pressure) (Pa), Pc: anintake valve downstream pressure (that is, cylinder pressure) (Pa): andT0: an intake valve upstream temperature (for example, an intakemanifold temperature Tm) (K).

[0104] VEL realizing volume flow ratio TQH0VEL is obtained by dividingthe air amount passing through intake valve 105 by engine rotation speedNe and discharge amount VOL#. Therefore, it can be also represented byequations (3) and (4). $\begin{matrix}{{{At}\quad {choke}\text{:}}\quad} & \quad \\{{{{TQH0VEL} = {\frac{{Cd} \cdot {Av} \cdot {P0}}{{{Ne} \cdot {VOL}}\quad {\# \cdot \sqrt{R \cdot {T0}}}}\sqrt{\gamma}\left( \frac{2}{\gamma - 1} \right)^{\frac{\gamma + 1}{2{({\gamma - 1})}}}}}{{At}\quad {no}\quad {choke}\text{:}}}\quad} & (3) \\{{TQH0VEL} = {\frac{{Cd} \cdot {Av} \cdot {P0}}{{{Ne} \cdot {VOL}}\quad {\# \cdot \sqrt{R \cdot {T0}}}}\left( \frac{Pc}{P0} \right)^{\frac{1}{\gamma}}\sqrt{\frac{2\gamma}{\gamma - 1}\left( {1 - \left( \frac{Pc}{P0} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}}} & (4)\end{matrix}$

[0105] Consequently, if valve upstream temperature Tm, valve upstreampressure Pm and cylinder pressure Pc have been already known,Cd·Av/(Ne·VOL#) is calculated to be converted into A·Cd/N/Vcharacteristic, so that state amount VACDNV equivalent to valve openingarea (Av) can be obtained. Therefore, in this embodiment, a table TVACDNas shown in the figure has been previously prepared, and by retrievingthis table, based on VEL realizing volume flow ratio TQH0VEL, theconversion into A·Cd/N/V characteristic is performed. Note, the tableTVACDNV is prepared in the following manner.

[0106] Namely, since VEL realizing volume flow ratio TQH0VEL can bedetermined, at the choke time, from the equation (3) as a valuecorresponding to Cd·Av/(Ne·VOL#) and a differential pressure ratio(Pc/P0) between fore and after the intake valve, and can be determined,at the no choke time, from the equation (4) as a value proportional toCd·Av/(Ne·VOL#), the map is prepared by obtaining a correlation betweenTQH0VEL and Cd·Av/(Ne·VOL#) by the simulation, experiment or the like.

[0107] Then, thus obtained VADCNV is multiplied by engine rotation speedNe at C part, and further multiplied by discharge amount VOL# at D part,to calculate a flow amount characteristic TVELAA0 (=Av.Cd). This TVELAA0corresponds to the opening area basically requested for the intake valve(to be referred to as basic requested valve opening area hereafter).

[0108] At E part, a VTC based correction is performed on basic requestedvalve opening area TVELAA0. Specifically, basic requested valve openingarea TVELAA0 is divided by valve timing based correction value KHOSIVCcorresponding to closing timing of intake valve, to calculate TVELAA1.When the valve timing (closing timing IVC) of intake valve is advanced,an effective cylinder volume is decreased so that the volume flow ratiois reduced even in the same valve opening area. In order to cope withthis, basic requested valve opening area TVELAA0 is corrected. Thesetting of valve timing based correction value KHOSIVC will be describedlater (refer to FIG. 16).

[0109] At F part, TVELAA1 calculated at E part is correctedcorresponding to the upstream pressure of intake valve 105 (to be simplyreferred to as valve upstream pressure hereafter). Specifically, TVELAA1is multiplied by valve upstream pressure based correction value KMANIP,to calculate TVELAA2. The volume flow ratio is changed due to a negativepressure generated in accordance with throttle opening. The valveopening area corresponding to such a change is obtained.

[0110] At the time of throttle-less control in which throttle valve 103b is fully opened, since the valve upstream pressure equals to theatmospheric pressure, the correction corresponding to the upstreampressure is unnecessary. However, actually, throttle valve 103 b isthrottled in response to a request of negative pressure for purging andthe like, such a correction is necessary. The setting of this valveupstream pressure based correction value KMANIP will be described later(refer to FIG. 17).

[0111] At G part, TVELAA2 calculated at F part is correctedcorresponding to engine rotation speed Ne. Specifically, TVELAA2 isdivided by a VEL opening area rotating correction value KHOSNE, tocalculate TVELAA. From the property of variable valve mechanism (VEL)112, an inertial force is increased due to the increase of enginerotation speed Ne, resulting in that the valve lift amount (valveopening area) is increased by the inertial force even in the same VELoperating angle. Therefore, the increased portion is corrected. Note,VEL opening area rotating correction value KHOSNE used for such acorrection is calculated by retrieving, at g1 part, a table TKHOSNE asshown in the figure based on engine rotation speed Ne.

[0112] At H part, using a table TTGVEL0 as shown in the figure, targetvalve opening area TVELAA is converted into a VEL operating angleTGVEL0. In the table TTGVEL0, a relation between the valve operatingangle (lift amount) and the valve opening area has been previouslyobtained.

[0113] Target valve opening area TVELAA is calculated as the flow amountcharacteristic including valve flow loss coefficient Cd, as a matter ofform. However, since valve flow loss coefficient Cd is determined basedon the valve operating angle (lift amount) in this embodiment, theconversion table TTGVEL0 is set inclusive of valve flow loss coefficientCd, to directly calculate target valve operating angle TGVEL0 based onthe flow amount characteristic equivalent to the valve opening area(that is, target valve opening area TVELAA).

[0114] As shown in FIG. 15 (corresponding to H part), valve flow losscoefficient Cd may be calculated by retrieving a table TCd based onvalve operating angle (VCS-ANGL) (at h1 part), a valve opening areaTVELAA′ may be calculated by dividing target valve opening area (thatis, the flow amount characteristic equivalent to valve opening area)TVELAA by valve flow loss coefficient Cd (at h2 part), and then targetoperating angle TGVEL0 may be calculated based on valve opening areaTVELM′ (h3 part).

[0115] In such a case, since valve flow loss coefficient Cd is changedin accordance with the flow amount at the time, the correction accordingto engine rotation speed Ne may be performed. Specifically, as indicatedby dotted line in the figure, a valve flow loss dynamic correctioncoefficient DHOSCD is calculated by retrieving a table TDHOSCD based onengine rotation speed Ne (at h4 part), to multiply this on TVELAA′ (ath5 part). Thereby, valve flow loss coefficient Cd is corrected accordingto engine rotation speed Ne. Valve flow loss dynamic correctioncoefficient DHOSCD may be directly multiplied on valve flow losscoefficient Cd.

[0116] Then, at I part, VEL operating angle TGVEL0 converted at H partis compared with an upper limit VEL operating angle (upper limit valveoperating characteristic) VELHLMT of variable valve mechanism (VEL) 112,to set a target VEL operating angle TGVEL. Specifically, as shown in thefigure, if TGVEL0>VELHLMT, VELHLMT is set as target VEL operating angleTGVEL. If TGVEL0<VELHLMT, TGVEL0 is set as target VEL operating angleTGVEL.

[0117] This is because, since the accuracy of intake air amount controlby variable valve mechanism (VEL) 112 is degraded under a state wherethere is no substantial differential pressure ratio between fore andafter the valve (that is, intake valve 105 is almost fully opened), theupper limit value of valve operating characteristic is set to preventthe accuracy degradation and also a valve operating characteristiccapable of ensuring the volume efficiency is set as much as possible.Accordingly, upper limit VEL operating angle VELHLMT is set as a maximumoperating angle capable of maintaining the accuracy of intake air amountcontrol.

[0118] Consequently, it is possible to maintain the high volumeefficiency while ensuring the accuracy of intake air amount controlmainly by variable valve mechanism (VEL) 112.

[0119] Maximum VEL operating angle VELHLMT is calculated by retrieving,at i1 part, a table TVELHLMT as shown in the figure based on enginerotation speed Ne.

[0120] As a result, control unit (C/U) 114 feedback controls actuator121, so that an actual VEL operating angle (VCS-ANGL) of control shaft16 in variable valve mechanism (VEL) 112 reaches target VEL operatingangle (TGVEL).

[0121] (c-2) Calculation of Valve Timing Based Correction Value KHOSIVC

[0122] The calculation of valve timing based correction value KHOSIVC tobe used at E part in FIG. 14 will be described referring to a controlblock diagram in FIG. 16.

[0123] In FIG. 16, at e1 part, by referring to a table TV0IVC as shownin the figure, an angle V0IVC in intake valve closing timing at the timewhen variable valve timing mechanism (VTC) 113 does not operate, thatis, at the VTC most retarded time, is obtained based on operating angleVCS-ANGL of variable valve mechanism (VEL) 112.

[0124] Next, at e2 part, an actual IVC angle REALIVC is obtained bysubtracting a rotation phase VTCNOW of intake side camshaft 13 fromV0IVC.

[0125] Then, at e3 part, by retrieving a table TKHOSIVC as shown in thefigure based on actual IVC angle REALIVC, a valve timing basedcorrection value KHOSIVC is set to be output to E part in FIG. 14.

[0126] Note, valve timing based correction value KHOSIVC includes: (1) astatic correction (correction of decreased portion of effective cylindervolume); (2) a dynamic correction (considering that, during enginerotating, air amount of the effective cylinder equivalent volume at IVCcannot be sucked, the effective cylinder equivalent volume is madevariable by the valve lift amount within a range of 0 to 100%); and (3)a correction of valve overlap (the correction corresponding to openingtiming IVO of intake valve 105). (Namely, the table TKHOSIVC is setinclusive of the factors of (1) to (3).)

[0127] (c-3) Setting of Valve Upstream Pressure Based Correction ValueKMANIP

[0128] Next, there will be described the setting of valve upstreampressure based correction value KMANIP to be used at F part in FIG. 14,referring to a control block diagram in FIG. 17.

[0129] In FIG. 17, it is required to establish the following equations(5) and (6) from the equation of the one-dimensional steady flow ofcompressed fluid, in order to keep the air amount passing through intakevalve 105 constant even if the valve upstream pressure (intake manifoldpressure) is changed (Pm0 to Pm1) by throttling throttle valve 103 b.$\begin{matrix}{{{At}\quad {choke}\text{:}}\quad} & \quad \\{{{{\frac{{Cd0} \cdot {Av0} \cdot {Pm0}}{\sqrt{R \cdot {Tm}}}\sqrt{\gamma}\left( \frac{2}{\gamma - 1} \right)^{\frac{\gamma + 1}{2{({\gamma - 1})}}}} = {\frac{{Cd1} \cdot {Av1} \cdot {Pm1}}{\sqrt{R \cdot {Tm}}}\sqrt{\gamma}\left( \frac{2}{\gamma - 1} \right)^{(\frac{\gamma + 1}{2{({\gamma - 1})}})}}}{{At}\quad {no}\quad {choke}\text{:}}}\quad} & (5) \\{{\frac{{Cd0} \cdot {Av0} \cdot {Pm0}}{\sqrt{R \cdot {Tm}}}\left( \frac{Pc0}{Pm0} \right)^{\frac{1}{\gamma}}\sqrt{\frac{2\gamma}{\gamma - 1}\left( {1 - \left( \frac{Pc0}{Pm0} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}} = {\frac{{Cd1} \cdot {Av1} \cdot {Pm1}}{\sqrt{R \cdot {Tm}}}\left( \frac{Pc1}{Pm1} \right)^{\frac{1}{\gamma}}\sqrt{\frac{2\gamma}{\gamma - 1}\left( {1 - \frac{Pc1}{Pm1}} \right)^{\frac{\gamma - 1}{\gamma}}}}} & (6)\end{matrix}$

[0130] In the above equations, Pm0: valve upstream pressure at the timewhen throttle valve is fully opened (intake manifold pressuresubstantially equals atmospheric pressure), Pm1: valve upstream pressureat the time of target Boost (intake manifold pressure), Pc0: valvedownstream pressure at the time when throttle valve is fully opened(substantially equals cylinder pressure), Pc1: valve downstream pressureat the time of target Boost (substantially equals cylinder pressure),Av0: intake valve opening area at the time when throttle valve is fullyopened, and Av1: intake valve opening area at the time of target Boost.

[0131] Accordingly, valve upstream pressure based correction valueKMANIP relative to valve opening area Av0 at the time when the valveupstream pressure equals the atmospheric pressure (Pm0) is representedby the following equations (7) and (8). $\begin{matrix}{{{At}\quad {choke}\quad {time}\text{:}}\quad} & \quad \\{{{{KMANlP} = {\frac{{Cd1} \cdot {Av1}}{{Cd0} \cdot {Av0}} = \frac{Pm0}{Pm1}}}{{At}\quad {no}\quad {choke}\text{:}}}\quad} & (7) \\{{KMANlP} = {\frac{{Cd1} \cdot {Av1}}{{Cd0} \cdot {Av0}} = \frac{{{Pm0}\left( \frac{Pc0}{Pm0} \right)}^{\frac{1}{\gamma}}\sqrt{\left( {1 - \left( \frac{Pc0}{Pm0} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}}{{{Pm1}\left( \frac{Pc1}{Pm1} \right)}^{\frac{1}{\gamma}}\sqrt{\left( {1 - \left( \frac{Pc1}{Pm1} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}}}} & (8)\end{matrix}$

[0132] Consequently, valve upstream pressure based correction valueKMANIP is primarily determined by the atmospheric pressure/target Boost(manifold pressure) at the choke time. Further, since it is consideredthat (Pc0/Pm0) substantially equals (Pc1/Pm1), the atmosphericpressure/target Boost becomes dominative even at no choke time. Ineither of the cases, valve upstream pressure based correction valueKMANIP can be made the atmospheric pressure/target Boost.

[0133] Therefore, in this embodiment, at f1 part in FIG. 17, theatmospheric pressure/target Boost (target manifold pressure) is set by asingle point constant as valve upstream pressure based correction valueKMANIP, to be output to F part in FIG. 14. Note, in the embodiment,since the target Boost is made constant (88 KPa), a fixed value (101.3KPa/88 KPa) is output as valve upstream pressure based correction valueKMANIP.

[0134] However, in the case where target volume flow TQH0ST is equal toor less than minimum volume flow ratio QH0LMT, that is in the case whereminimum volume flow ratio QH0LMT is selected at A part in FIG. 14,regardless of the valve upstream pressure, 1.0 is output as valveupstream pressure based correction value KMANIP so that the valveoperating angle equivalent to minimum volume flow ratio QH0LMT can befinally obtained (correction is not performed).

[0135] (d) Calculation of Target Throttle Opening TDTVO

[0136] Basically, the intake air amount control is performed by thecontrol of variable valve mechanism (VEL) 112. However, in order togenerate a requested negative pressure or in order to assist the intakeair amount control by variable valve mechanism (VEL) 112, the throttlecontrol is executed. The target throttle opening calculating section “c”calculates a target throttle opening TDVTC in the following manner.

[0137] Firstly, when intake valve 105 has a standard valve operatingcharacteristic (in this embodiment, the valve operating characteristicof when variable valve mechanism (VEL) 112 does not operate), an openingarea TVOAA0 of throttle valve 103 b required for generating apredetermined negative pressure (to be referred to as standard requestedthrottle opening area hereafter) is calculated, and corrected inaccordance with an actual change in valve operating characteristic of(controlled) intake valve 105, to be made a target throttle opening areaTVOAA. Then, target throttle opening TDTVO is calculated based on targetthrottle opening area TVOAA. There will be described the calculation inthe target throttle opening calculating section “d”, based on FIG. 18 toFIG. 20.

[0138] (d-1) Setting of Target Throttle Opening TDTVO

[0139] In FIG. 18, at J part, a state amount TADNV0 equivalent to anopening area At of throttle valve 103 b requested at the standard valveoperating characteristic is calculated. Specifically, TADNV0 iscalculated by retrieving a conversion table TTADNV0 as shown in thefigure, based on target volume flow ratio TQH0ST. This state amountTADNV0 is represented by TADNV0=At/(Ne·VOL#) when the throttle openingarea is At, the engine rotation speed is Ne, and the discharge amount(cylinder volume) is VOL#.

[0140] Then, calculated TADNV0 is multiplied by engine rotation speed Neat K part, and further multiplied by discharge amount VOL# at L part, tocalculate standard requested throttle opening area TVOAA0.

[0141] At M part, a correction according to a change in operatingcharacteristic of intake valve 105 is performed on calculated standardrequested throttle opening area TVOAA0. Specifically, standard requestedthrottle opening area TVOAA0 is multiplied by an intake valve openingbased correction value KAVEL, to be made target throttle opening areaTVOAA. The setting of intake valve opening based correction value KAVELwill be described later (refer to FIG. 19).

[0142] At N part, target throttle opening TDTVO is set by retrieving aconversion table TTDTVO as shown in the figure, based on calculatedtarget throttle opening area TVOAA.

[0143] As a result, control unit (C/U) 114 controls electronicallycontrolled throttle 104 so that an actual opening of throttle valve 104becomes target throttle opening TDTVO.

[0144] (d-2) Calculation of Intake Valve Opening Based Correction ValueKAVEL

[0145] Next, the calculation of intake valve opening based correctionvalue KAVEL to be used at F part in FIG. 18 will be described referringto a control block diagram in FIG. 19.

[0146] In FIG. 19, at first, an air flow amount Qth (t) (kg/sec) passingthrough throttle valve 103 b can be represented by the followingequations (9) and (10) from the equation of the one dimensional steadyflow of compressed fluid. $\begin{matrix}{{{{At}\quad {choke}\quad {time}\text{:}\quad \frac{Pc}{Pm}} \leq \left( \frac{2}{\gamma + 1} \right)^{\frac{\gamma}{\gamma - 1}}}\quad} & \quad \\{{{{{Qth}(t)} = {\frac{{At} \cdot {Pa}}{\sqrt{R \cdot {Ta}}}\sqrt{\gamma}\left( \frac{2}{\gamma - 1} \right)^{\frac{\gamma + 1}{2{({\gamma - 1})}}}}}{{At}\quad {no}\quad {choke}\text{:}}}\quad} & (9) \\{{{Qth}(t)} = {\frac{{At} \cdot {Pa}}{\sqrt{R \cdot {Ta}}}\left( \frac{Pm}{Pa} \right)^{\frac{1}{\gamma}}\sqrt{\frac{2\gamma}{\gamma - 1}\left( {1 - \left( \frac{Pm}{Pa} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}}} & (10)\end{matrix}$

[0147] In the above equations, Pa: atmospheric pressure (Pa), Pm:manifold pressure (Pa), Ta: outside air temperature, and At: throttleopening area (m₂).

[0148] Thereby, in order to keep the air amount constant even if theoperating characteristic of intake valve 105 is changed (from state 0 tostate 1), the following equation (11) is required to be established.$\begin{matrix}{{\frac{{At0} \cdot {Pa}}{\sqrt{R \cdot {Ta}}}\left( \frac{{Pm}^{\prime}0}{Pa} \right)^{\frac{1}{\gamma}}\sqrt{\frac{2\gamma}{\gamma - 1}\left( {1 - \left( \frac{{Pm}^{\prime}0}{Pa} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}} = {\frac{{At1} \cdot {Pa}}{\sqrt{R \cdot {Ta}}}\left( \frac{{Pm}^{\prime}1}{Pa} \right)^{\frac{1}{\gamma}}\sqrt{\frac{2\gamma}{\gamma - 1}\left( {1 - \frac{{Pm}^{\prime}1}{Pa}} \right)^{\frac{\gamma - 1}{\gamma}}}}} & (11)\end{matrix}$

[0149] In the above equation, Pa: atmospheric pressure, Ta: outside airtemperature, Pm′0: intake manifold pressure at standard valve operatingcharacteristic, Pm′1: intake manifold pressure at the time when variablevalve mechanism (VEL) operates, At0: throttle opening area at standardvalve operating characteristic, and At1: throttle opening area at thetime when variable valve mechanism (VEL) operates.

[0150] Accordingly, intake valve opening based correction value KAVELrelative to throttle opening area At0 at standard valve operatingcharacteristic is represented by the following equation (12).$\begin{matrix}{{KAVEL} = {\frac{At1}{At0} = \frac{\left( \frac{{Pm}^{\prime}0}{Pa} \right)^{\frac{1}{\gamma}}\sqrt{\left( {1 - \left( \frac{{Pm}^{\prime}0}{Pa} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}}{\left( \frac{{Pm}^{\prime}1}{Pa} \right)^{\frac{1}{\gamma}}\sqrt{\left( {1 - \left( \frac{{Pm}^{\prime}1}{Pa} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}}}} & (12)\end{matrix}$

[0151] Therefore, in the embodiment, at m1 part in FIG. 19, a pressureratio (Pm′0/Pa) at standard valve operating characteristic is obtainedby referring to a map previously allotted in performance as shown in thefigure, based on target volume flow ratio TQH0ST and engine rotationspeed Ne.

[0152] Then, at m2 part, a coefficient KAP0 is calculated by retrievinga table TBLKAP0 as shown in the figure, based on the pressure ratio(Pm′0/Pa) at standard valve operating characteristic. Note, thiscoefficient KAP0 can be represented by the following equation (13) andcorresponds to a value of the numerator in the equation (12).$\begin{matrix}{{KAP0} = {\left( \frac{{Pm}^{\prime}0}{Pa} \right)^{\frac{1}{\gamma}}\sqrt{\left( {1 - \left( \frac{{Pm}^{\prime}0}{Pa} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}}} & (13)\end{matrix}$

[0153] Further, a pressure ratio (Pm′1/Pa) at the time when variablevalve mechanism (VEL) 112 operates is calculated in the followingmanner.

[0154] Firstly, an air amount (actual intake air amount) Qacyl suckedinto cylinder can be represented by the following equation (14) assumedthat a new air rate is η. $\begin{matrix}{{Qacyl} = {{\frac{VOL}{R \cdot {Ta}} \cdot \eta \cdot {Pm}^{\prime}}1}} & (14)\end{matrix}$

[0155] Thus, the pressure ratio (Pm′1/Pa) becomes the following.$\begin{matrix}{\frac{{Pm}^{\prime}1}{Pa} = {\frac{{Qacyl} \cdot R \cdot {Ta}}{{VOL} \cdot \eta \cdot {Pa}} = {{\frac{TP}{\eta} \cdot \frac{R \cdot {Ta}}{{VOL} \cdot {Pa}}} = \frac{TP}{\eta \cdot {TP100V}}}}} & (15)\end{matrix}$

[0156] In the above equation, “TP” is an air amount (actual intake airamount) Qacyl sucked in the cylinder, “TP100V” is an air amount suckedinto the cylinder at the time when throttle valve 103 b is fully openedand is calculated by TP100V=(VOL·Pa)/(R·Ta). Further, “VOL” is aneffective cylinder volume at each valve operating characteristic ofintake valve 105.

[0157] Accordingly, by obtaining TP, TP100 and new air rate η, pressureratio (Pm′1/Pa) can be calculated without the necessity of detectingintake manifold pressure Pm′.

[0158] Therefore, in the embodiment, at m3 part, a conversion constantTPGAIN# is multiplied on a ratio WQH0VEL of volume flow passed throughintake valve 105 at each operating characteristic at the time whenthrottle valve 103 b is fully opened, and the unit conversion isperformed to calculate TP100V. The calculation of ratio WQH0VEL ofpassed volume flow will be described later (refer to FIG. 20).

[0159] Further, at m4 part, new air rate η is calculated by referring toa map previously allotted in performance as shown in the figure, basedon a ratio RQH0VEL of volume flow passed through intake valve 105(actual engine volume flow ratio) at each operating characteristic atthe time when throttle valve 103 b is throttled (at the time when thevalve upstream pressure is generated) and engine rotation speed Ne. Thecalculation of actual engine volume flow ratio RQH0VEL will be describedlater (refer to FIG. 20).

[0160] However, new air rate η is not limited to the one calculated asabove, and may be estimated based on operating conditions, for example.

[0161] Then, at m5 part, actual intake air amount “TP” is multiplied bynew air rate η, to calculate “TP100V·η”, and further, at m6 part,“TP/(TP100V·η)” is calculated. The resultant corresponds to pressureratio (Pm′1/Pa) at the time when variable valve mechanism (VEL) 112operates.

[0162] Thus, in this embodiment, pressure ratio (Pm′1/Pa) betweenmanifold pressure and atmospheric pressure can be obtained without thenecessity of detecting intake manifold pressure Pm. In the case where apressure sensor detecting intake manifold pressure Pm is provided,pressure ratio (Pm′1/Pa) may be calculated using a detection value ofthe pressure sensor.

[0163] Further, at m7 part, a coefficient KAP1 is calculated byretrieving a table TKPA1 as shown in the figure, based on pressure ratio(Pm′1/Pa) at the time when variable valve mechanism (VEL) 112 operates.This coefficient KAP1 can be represented by the following equation (16)and corresponds to a value of the denominator in the equation (12).$\begin{matrix}{{KAP1} = {\left( \frac{{Pm}^{\prime}1}{P\quad a} \right)^{\frac{1}{\gamma}}\sqrt{\left( {1 - \left( \frac{{Pm}^{\prime}1}{P\quad a} \right)^{\frac{\gamma - 1}{\gamma}}} \right)}}} & (16)\end{matrix}$

[0164] At m8 part, by dividing coefficient KAP0 calculated at m2 part bycoefficient KAP1 calculated at m7 part, to set intake valve openingbased correction value KAVEL, and the set value is output to M part inFIG. 17.

[0165] (d-3) Calculations of Ratio WQHOVEL of Volume Flow Passed ThroughIntake Valve 105 at the Time When Throttle Valve 103 b is Fully Opened,and of Actual Engine Volume flow Ratio RQH0VEL

[0166] These calculations are performed by obtaining the opening area ofintake valve 105 based on the operating angles of variable valvemechanism (VEL) 112 and variable valve timing mechanism (VTC) 114 andconverting the opening area to the volume flow ratio.

[0167] In FIG. 20, at m10 part, an opening area AAVEL0 of intake valve105 is calculated by retrieving a table TMVEL0 as shown in the figure,based on operating angle VCS-ANGL of variable valve mechanism (VEL) 112.

[0168] At m11 part, in the same manner as G part in FIG. 14, VEL openingarea is rotatingly corrected according to engine rotation speed Ne, tocalculate AAVEL.

[0169] Calculated AAVEL is divided by engine rotation speed Ne at m12part, and further divided by discharge amount (cylinder volume) VOL# atm13 part, to be made an A/N/V characteristic.

[0170] At m14 part, a table TWH0VEL0 as shown in the figure isretrieved, to convert the A/N/V characteristic into a volume flow ratioWH0VEL0.

[0171] Then, at m15 part, in the same manner as E part in FIG. 14, theVTC based correction is performed to calculate ratio WQH0VEL of volumeflow passed through intake valve 105 at the time when throttle valve 103b is fully opened, and the resultant is output to m3 part in FIG. 19.

[0172] On the other hand, at m16 part, AAVEL calculated at m11 part ismultiplied by the ratio between actual intake manifold pressure Pm andatmospheric pressure Pa (Pm/Pa), to calculate AAVEL′.

[0173] Then, this AAVEL′ is divided by engine rotation speed Ne at m17part, and further divided by discharge amount (cylinder volume) VOL# atm18 part, to be made the A/N/V characteristic.

[0174] At m19 part, in the same manner as m14 part, a table TRH0VEL0 asshown in the figure is retrieved to convert the A/N/V characteristicinto a volume flow ratio RH0VEL0.

[0175] Then, at m20 part, in the same manner as m15 part (E part in FIG.14), the VTC based correction is performed to calculate the actualvolume flow ratio RQH0VEL, and the resultant is output to m4 part inFIG. 19.

[0176] As described in the above, in this embodiment, a control in whichvariable valve mechanism (VEL) 112 and electronically controlledthrottle 104 are cooperative with each other is performed. Therefore, anintake air amount control (torque control) mainly by variable valvemechanism (VEL) 112 can be executed with high accuracy.

[0177] Next, other embodiment (second embodiment) of intake air amountcontrol to be executed by control unit (C/U) 114 will be described withreference to block diagrams of FIG. 21 to FIG. 24.

[0178] In this embodiment, intake valve 105 is controlled to a targetvalve operating characteristic. While, in a total opening area (anintegrated value of opening areas) obtained based on the target valveoperating characteristic, since the opening area during valve overlapperiod is an ineffective portion where air is not newly sucked, thetotal opening area is corrected with a correction value according to thevalve overlap to be made a total opening area (effective opening area)where air is newly sucked, so that the total opening area (effectiveopening area) indicative of intake air amount actually controlled byintake valve is compared with the target intake air amount to set atarget opening of throttle valve 103 b.

[0179] In FIG. 21, a target volume flow ratio calculating section 301calculates a target volume flow ratio TQH0ST (target intake air amount)of engine 101, in the same manner as the target volume flow ratiocalculating section “a” in the first embodiment.

[0180] In a VEL target angle calculating section 302, a target operatingangle TGVEL (target lift amount) of control shaft 16 in variable valvemechanism (VEL) 112 is calculated by referring to a map as shown in thefigure, based on target volume flow ratio TQH0ST and engine rotationspeed Ne. Here, in this embodiment, as with the VEL target operatingangle calculating section “c” in the first embodiment, the larger targetvolume flow ratio TQH0ST is and the higher engine rotation speed Ne is,the target operating angle is set such that the lift amount becomeslarger.

[0181] However, due to a minimum limit of lift amount, at the side oflow load and low rotation, a lift amount larger than a requested amountcorresponding to target volume flow ratio TQH0ST is set. Such an excessportion is corrected by the throttle control of throttle valve 103 asdescribed later.

[0182] In a VTC target angle calculating section 303, as with the VTCtarget angle calculating section “b” in the first embodiment, a targetphase angle TGVTC (target advance amount) in variable valve timingmechanism (VTC) 113 is calculated based on target volume flow ratioTQH0ST and engine rotation speed Ne. Here, the larger target volume flowratio TQH0ST is and the higher engine rotation speed Ne is, the targetvalve timing is retarded.

[0183] Then, target operating angle TGVEL is input to a valve totalopening area calculating section 304, to be converted into the totalopening area of intake valve 105 of when variable valve mechanism (VEL)112 is controlled based on target operating angle TGVEL. Note, the totalopening area is an integral value of valve opening area during a closingperiod of intake valve 105.

[0184] On the other hand, in FIG. 22, in a VTC most retarded time IVOcalculating section 305, variable valve mechanism (VEL) 112 iscontrolled based on target operating angle TGVEL, and also openingtiming IVO of intake valve 105 assuming that the valve timing iscontrolled to the most retarded side by variable valve timing mechanism(VTC) 113, is calculated.

[0185] Opening timing IVO calculated in VTC most retarded time IVOcalculating section 305 is added with a target phase angle TGVTC by anadder 306. Thereby, opening timing TGIVO of when the operatingcharacteristic of intake valve 105 is controlled based on targetoperating angle TGVEL and target phase angle TGVTC, is obtained.

[0186] The opening timing TGIVO is input to an O/L time basic areacalculating section 307.

[0187] In O/L time basic area calculating section 307, a basic value ofopening area integral value of intake valve 105 during the valve overlapperiod between intake valve 105 and exhaust valve 107 is obtained basedon opening timing TGIVO, since the closing timing of exhaust valve 107is fixed. The basic value is obtained in conformity with the case wherethe valve lift amount is smallest.

[0188] Further, in an O/L time area VEL correctively calculating section308, a correction coefficient in order to cope with a difference ofopening area due to a difference of lift amount is set based on targetoperating angle TGVEL.

[0189] In this embodiment, as opening timing IVO of intake valve 105 ischanged, the valve lift amount is changed, and even if the valve overlapperiod is the same, the opening area during the overlap period becomeslarge as the lift amount is larger (refer to FIG. 25). Therefore,correction coefficient (>1.0) is set to be a larger value as theoperating angle (lift amount) becomes larger.

[0190] The correction coefficient calculated in O/L time area VELcorrectively calculating section 308 is input to a switching outputsection 309. In switching output section 309, either the correctioncoefficient calculated in O/L time area VEL correctively calculatingsection 308 or 1.0 being a reference value of the correction coefficientis selectively output, depending on whether or not opening timing TGIVO(advance value from top dead center TDC to opening timing IVO) exceeds apredetermined angle (for example, 20 degrees).

[0191] As described above, even if the valve overlap period is the same,the opening area of intake valve 105 during the valve overlap period ischanged depending on the lift amount. However, if the valve overlapperiod is short, there does not occur a large difference in the openingarea depending on a difference between the lift amount (refer to FIG.25).

[0192] Therefore, in switching output section 309, when opening timingTGIVO is equal to or less than the predetermined angle and the valveoverlap period is equal to or less than the predetermined angle, 1.0being the reference value is output as the correction coefficient. Whenopening timing TGIVO exceeds the predetermined angle and the valveoverlap period exceeds the predetermined angle, the correctioncoefficient calculated in O/L time area VEL correctively calculatingsection 308 is output.

[0193] The correction coefficient output from switching output section309 is multiplied on the basic value of opening area integral value ofintake valve 105 in the valve overlap period calculated by O/L timebasic area calculating section 307.

[0194] Then, the opening area integral value in the valve overlap periodbeing the resultant of multiplicative calculation in adder 310 issubtracted from the total opening area calculated in valve total openingarea calculating section 304, and the integral value of opening area inthe opening period of intake valve 105 except for the valve overlapperiod is obtained.

[0195] The calculation result in a subtracter 311 is output to amultiplier 312, wherein the calculation result in subtracter 311 ismultiplied by the correction coefficient calculated in a VEL openingarea rotating correction calculating section 313, to be output aseffective opening area TVELAA0.

[0196] VEL opening area rotating correction calculating section 313 setsa larger correction coefficient ((>1.0), as engine rotation speed Ne ishigher.

[0197] In variable valve mechanism (VEL) 112, as described in the firstembodiment, there is a tendency that the valve lift amount becomeslarger than a target due to inertial force, as engine rotation speed Nebecomes higher. Due to this, there occurs an error difference betweenthe opening area calculated based on target operating angle TGVEL andtarget phase angle TGVTC, and the actual opening area. Therefore, in VELopening area rotating correction calculating section 313, a correctioncoefficient is set in order to increasingly correct the opening area ofintake valve 105 coping with the tendency that the valve lift amountbecomes larger than the target, as engine rotation speed Ne is higher.

[0198] In FIG. 23, in a flow loss correction coefficient calculatingsection 314, a flow loss coefficient Cd is calculated based on targetoperating angle TGVEL (target valve lift amount).

[0199] Then, in an adder 315, effective opening area TVELAA0 ismultiplied by flow loss coefficient Cd, to perform a correction copingwith a difference between flow losses due to valve lift amount.

[0200] Effective opening area TVFELAA0 subjected to the correction byflow loss coefficient Cd is divided by effective discharge amount(cylinder total volume) VOL# in a divider 316, and further divided byengine rotation speed Ne in a divider 317, to be converted into a stateamount AANV. Further, state amount AANV is converted into volume flowratio TQH0VE of intake valve 105 in a conversion section 318.

[0201] Note, volume flow ratio TQH0VEL of intake valve 105 is a value onthe condition of the full open state of throttle valve 103 b.

[0202] In FIG. 24, in a divider 319, target volume flow ratio TQH0ST isdivided by volume flow ratio TQH0VEL, to calculate volume flow ratio QH0required for throttle valve 103 b in order to obtain target volume flowratio TQH0ST.

[0203] Volume flow ratio QH0 required for throttle valve 103 b isconverted into state amount AANV in a conversion section 320, and ismultiplied by effective discharge amount (cylinder total volume) VOL# ina multiplier 321 and further multiplied by engine rotation speed Ne in amultiplier 322, to be converted into opening area AA required forthrottle valve 103 b.

[0204] Then, opening area M is converted into an angle (opening) ofthrottle valve 103 b in a conversion section 323, and the angle isoutput as target angle TGTVO so that electronically controlled throttle104 is controlled based on target angle TGTVO.

[0205] As described above, in this embodiment, volume flow ratio TQH0VELactually obtained with the lift amount and valve timing of intake valve105 is converted from the effective opening area (total opening areaafter correction) of intake valve 105 considering the ineffectiveopening area during the valve overlap period. Target volume flow ratioTQH0ST is divided by volume flow ratio TQH0VEL, to obtain requestedvolume flow ratio QH0 of throttle valve 103 b, and this requested volumeflow ratio QH0 is converted into the target opening of throttle valve103 b.

[0206] Thus, the valve operating characteristic (lift amount and valvetiming) of intake valve 105 is controlled based on the target intake airamount (target volume flow ratio TQH0ST), and also the intake air amount(volume flow ratio) actually obtained with the valve operatingcharacteristic of intake valve 105 is predicted based on the valveoverlap, so that the excess portion (error amount due to valve overlap)to the target intake air amount (target volume flow ratio TQH0ST) can becorrected by the throttle control of throttle valve 103 b. Thereby, thecontrol to the target intake air amount (target volume flow ratioTQH0ST) can be performed with high accuracy.

[0207] The entire contents of Japanese Patent Applications No.2001-315386 filed Oct. 12, 2001, No. 2001-320953 filed Oct. 18, 2001,No. 2001-342176 filed Nov. 7, 2001 and No. 2001-388160 filed Dec. 20,2001, each priority of which is claimed, are incorporated herein byreference.

What is claimed are:
 1. An apparatus for controlling an intake airamount of an internal combustion engine provided with a variable valvemechanism that varies at least a valve operating characteristic of anintake valve, comprising: an operating condition detecting sensordetecting operating conditions of said engine; a valve operatingcharacteristic detecting sensor detecting said valve operatingcharacteristic; and a control unit that sets a target intake air amountequivalent to a target torque according to the operating conditions ofthe engine, sets a target valve operating characteristic based on theset target intake air amount, and controls said variable valve mechanismso that an actual valve operating characteristic reaches said targetvalve operating characteristic.
 2. An apparatus for controlling anintake air amount of an internal combustion engine according to claim 1,wherein said internal combustion engine is provided with a throttlevalve driven to open and close by an actuator, in addition to saidvariable valve mechanism; said apparatus further comprises a throttleopening sensor detecting an opening of said throttle valve; and saidcontrol unit controls said variable valve mechanism so that the actualvalve operating characteristic reaches said target valve operatingcharacteristic, and sets a target throttle opening of said throttlevalve based on said target intake air amount and said valve operatingcharacteristic, to control said actuator so that an actual throttleopening reaches said target throttle opening.
 3. An apparatus forcontrolling an intake air amount of an internal combustion engineaccording to claim 1, wherein said control unit sets said target intakeair amount based on an accelerator opening and an engine rotation speed.4. An apparatus for controlling an intake air amount of an internalcombustion engine according to claim 1, wherein, when said target intakeair amount is equal to or less than a minimum intake air amountcontrollable by said variable valve mechanism, said control unit setssaid target valve operating characteristic based on the minimum intakeair amount.
 5. An apparatus for controlling an intake air amount of aninternal combustion engine according to claim 4, wherein said minimumintake air amount is calculated based on an engine rotation speed.
 6. Anapparatus for controlling an intake air amount of an internal combustionengine according to claim 1, wherein said control unit converts a targetvolume flow ratio equivalent to said target torque into a target valveopening area, and sets said target valve operating characteristic basedon the target valve opening area.
 7. An apparatus for controlling anintake air amount of an internal combustion engine according to claim 6,wherein said control unit corrects said target valve opening areaaccording to the valve operating characteristic, and sets said targetvalve operating characteristic based on the corrected target valveopening area.
 8. An apparatus for controlling an intake air amount of aninternal combustion engine according to claim 7, wherein said controlunit corrects said target valve opening area based on a flow loss amountaccording to a valve lift amount of said intake valve.
 9. An apparatusfor controlling an intake air amount of an internal combustion engineaccording to claim 8, wherein said control unit corrects said targetvalve opening area based on the flow loss amount according to the valvelift amount of said intake valve and also according to an enginerotation speed.
 10. An apparatus for controlling an intake air amount ofan internal combustion engine according to claim 7, wherein said controlunit corrects said target valve opening area according to actual closingtiming of said intake valve.
 11. An apparatus for controlling an intakeair amount of an internal combustion engine according to claim 6,wherein said control unit corrects said target valve opening areaaccording to an intake pressure on the intake valve upstream side, andsets said target valve operating characteristic based on the correctedtarget valve opening area.
 12. An apparatus for controlling an intakeair amount of an internal combustion engine according to claim 11,wherein, when said target volume flow ratio is equal to or less than aminimum volume flow ratio controllable by said variable valve mechanism,said control unit does not perform the correction according to theintake pressure on the intake valve upstream side.
 13. An apparatus forcontrolling an intake air amount of an internal combustion engineaccording to claim 6, wherein said control unit corrects said targetvalve opening area according to an engine rotation speed, and sets saidtarget valve operating characteristic based on the corrected targetvalve opening area.
 14. An apparatus for controlling an intake airamount of an internal combustion engine according to claim 1, wherein,when said target valve operating characteristic is equal to or above apredetermined upper limit valve operating characteristic, said controlunit controls said variable valve mechanism so that the actual valveoperating characteristic reaches said upper limit valve operatingcharacteristic.
 15. An apparatus for controlling an intake air amount ofan internal combustion engine according to claim 14, wherein said upperlimit valve operating characteristic is calculated based on an enginerotation speed.
 16. An apparatus for controlling an intake air amount ofan internal combustion engine according to claim 2, wherein said controlunit converts said target volume flow ratio equivalent to said targettorque into a requested throttle opening area requested for saidthrottle valve when said intake valve has a standard valve operatingcharacteristic, corrects the requested throttle opening area accordingto the actual valve operating characteristic, and sets said targetthrottle opening based on the corrected requested throttle opening area.17. An apparatus for controlling an intake air amount of an internalcombustion engine according to claim 16, wherein said control unitcorrects said requested throttle opening area based on a correctionvalue calculated based on a ratio between the atmospheric pressure andan intake pressure on the intake valve upstream side of when said intakevalve is the standard valve operating characteristic, and a ratiobetween the atmospheric pressure and an actual intake pressure on theintake valve upstream side.
 18. An apparatus for controlling an intakeair amount of an internal combustion engine according to claim 17,wherein said ratio between the atmospheric pressure and the actualintake pressure on the intake valve upstream side is calculated based onan actual intake air amount sucked into the engine, a throttle full-opentime intake air amount sucked into the engine at the time when saidthrottle valve is fully opened, and a new air rate set according tooperating conditions of the engine.
 19. An apparatus for controlling anintake air amount of an internal combustion engine according to claim 2,wherein said control unit predicts an actual intake air amountcontrolled by the intake valve based on the operating characteristic ofthe intake valve and the valve overlap at the operating characteristic,and sets said target throttle opening based on the predicted value andsaid target intake air amount.
 20. An apparatus for controlling anintake air amount of an internal combustion engine according to claim 2,wherein said control unit calculates a valve operating area of theintake valve at said target valve operating characteristic, corrects thevalve opening area based on a correction value according to the valveoverlap, and sets said target throttle opening based on the correctedvalve opening area and said target intake air amount.
 21. An apparatusfor controlling an intake air amount of an internal combustion engineaccording to claim 20, wherein said correction value according to thevalve overlap is set by correcting a basic correction value to be setbased on the valve overlap according to a valve lift amount.
 22. Anapparatus for controlling an intake air amount of an internal combustionengine according to claim 21, wherein said control unit does not performthe correction according to said valve lift amount when said valveoverlap amount is equal to or less than a predetermined amount.
 23. Anapparatus for controlling an intake air amount of an internal combustionengine according to claim 20, wherein said control unit corrects saidvalve opening area based on a correction value according to said valveoverlap, and also according to an engine rotation speed.
 24. Anapparatus for controlling an intake air amount of an internal combustionengine according to claim 20, wherein said control unit converts thecorrected valve opening area into a volume flow ratio, calculates arequested volume flow ratio in said throttle valve by dividing a targetvolume flow ratio equivalent to said target torque by the volume flowratio, and converts the requested volume flow ratio to set said targetthrottle opening.
 25. An apparatus for controlling an intake air amountof an internal combustion engine according to claim 24, wherein saidcorrected valve opening area is further corrected based on a flow lossvalue according to said valve lift amount, to be converted into thevolume flow ratio.
 26. An apparatus for controlling an intake air amountof an internal combustion engine according to claim 1, wherein saidvariable valve mechanism comprises a mechanism varying a valve liftamount of said intake valve and a mechanism varying valve timing, andsaid control unit sets a target valve lift amount and target valvetiming of said intake valve as said target valve operatingcharacteristic.
 27. An apparatus for controlling an intake air amount ofan internal combustion engine according to claim 26, wherein saidmechanism varying said valve lift amount includes: a drive shaftrotating in synchronism with a crankshaft; a drive cam fixed to saiddrive shaft; a swing cam swinging to operate said intake valve to openand close; a transmission mechanism with one end connected to said drivecam side and the other end connected to said swing cam side; a controlshaft having a control cam changing the position of said transmissionmechanism; and an actuator rotating said control shaft, and successivelychanges the valve lift amount of said intake valve by rotatinglycontrolling said control shaft by said actuator, and wherein saidmechanism varying said valve timing successively changes a rotationphase of said drive shaft relative to the crankshaft.
 28. An apparatusfor controlling an intake air amount of an internal combustion engineprovided with a variable valve mechanism that varies at least a valveoperating characteristic of an intake valve, comprising: operatingcondition detecting means for detecting operating conditions of saidengine; valve operating characteristic detecting means for detectingsaid valve operating characteristic; target intake air amount settingmeans for setting a target intake air amount equivalent to a targettorque according to the operating conditions of the engine; target valveoperating characteristic setting means for setting a target valveoperating characteristic based on said target intake air amount; andvariable valve mechanism control means for controlling said variablevalve mechanism so that an actual valve operating characteristic reachessaid target valve operating characteristic.
 29. A method of controllingan intake air amount of an internal combustion engine provided with avariable valve mechanism that varies at least a valve operatingcharacteristic of an intake valve, wherein a target intake air amountequivalent to a target torque is set according to the operatingconditions of the engine, a target valve operating characteristic is setbased on the set target intake air amount; and said variable valvemechanism is controlled so that an actual valve operating characteristicreaches said target valve operating characteristic.
 30. A method ofcontrolling an intake air amount of an internal combustion engineaccording to claim 29, wherein said internal combustion engine includesa throttle valve driven to open and close by an actuator, in addition tosaid variable valve mechanism; said variable valve mechanism iscontrolled so that an actual valve operating characteristic reaches saidtarget valve operating characteristic, and, also a target throttleopening of said throttle valve is set based on said target intake airamount and said valve operating characteristic, to control said actuatorso that an actual throttle opening reaches said target throttle opening.31. A method of controlling an intake air amount of an internalcombustion engine according to claim 29, wherein said target intake airamount is set based on an accelerator opening and an engine rotationspeed.
 32. A method of controlling an intake air amount of an internalcombustion engine according to claim 29, wherein, when said targetintake air amount is equal to or less than a minimum intake air amountcontrollable by said variable valve mechanism, said target valveoperating characteristic is set based on the minimum intake air amount.33. A method of controlling an intake air amount of an internalcombustion engine according to claim 32, wherein said minimum intake airamount is calculated based on an engine rotation speed.
 34. A method ofcontrolling an intake air amount of an internal combustion engineaccording to claim 29, wherein a target volume flow ratio equivalent tosaid target torque is converted into a target valve opening area, andsaid target valve operating characteristic is set based on the targetvalve opening area.
 35. A method of controlling an intake air amount ofan internal combustion engine according to claim 34, wherein said targetvalve opening area is corrected according to the valve operatingcharacteristic, and said target valve operating characteristic is setbased on the corrected target valve opening area.
 36. A method ofcontrolling an intake air amount of an internal combustion engineaccording to claim 35, wherein said target valve opening area iscorrected based on a flow loss amount according to a valve lift amountof said intake valve.
 37. A method of controlling an intake air amountof an internal combustion engine according to claim 36, wherein saidtarget valve opening area is corrected based on the flow loss amountaccording to the valve lift amount of said intake valve and alsoaccording to an engine rotation speed.
 38. A method of controlling anintake air amount of an internal combustion engine according to claim35, wherein said target valve opening area is corrected according toactual closing timing of said intake valve.
 39. A method of controllingan intake air amount of an internal combustion engine according to claim34, wherein said target valve opening area is corrected according to anintake pressure on the intake valve upstream side, and said target valveoperating characteristic is set based on the corrected target valveopening area.
 40. A method of controlling an intake air amount of aninternal combustion engine according to claim 39, wherein, when saidtarget volume flow ratio is equal to or less than a minimum volume flowratio controllable by said variable valve mechanism, the correctionaccording to the intake pressure on the intake valve upstream side isnot performed.
 41. A method of controlling an intake air amount of aninternal combustion engine according to claim 34, wherein said targetvalve opening area is corrected according to an engine rotation speed,and said target valve operating characteristic is set based on thecorrected target valve opening area.
 42. A method of controlling anintake air amount of an internal combustion engine according to claim29, wherein, when said target valve operating characteristic is equal toor above a predetermined upper limit valve operating characteristic,said variable valve mechanism is controlled so that the actual valveoperating characteristic reaches said upper limit valve operatingcharacteristic.
 43. A method of controlling an intake air amount of aninternal combustion engine according to claim 42, wherein said upperlimit valve operating characteristic is calculated based on an enginerotation speed.
 44. A method of controlling an intake air amount of aninternal combustion engine according to claim 30, wherein a targetvolume flow ratio equivalent to said target torque is converted into arequested throttle opening area requested for said throttle valve whensaid intake valve has a standard valve operating characteristic, therequested throttle opening area is corrected according to the actualvalve operating characteristic, and said target throttle opening is setbased on the corrected requested throttle opening area.
 45. A method ofcontrolling an intake air amount of an internal combustion engineaccording to claim 44, wherein said requested throttle opening area iscorrected based on a correction value calculated based on a ratiobetween the atmospheric pressure and an intake pressure on the intakevalve upstream side of when said intake valve is the standard valveoperating characteristic and a ratio between the atmospheric pressureand an actual intake pressure on the intake valve upstream side.
 46. Amethod of controlling an intake air amount of an internal combustionengine according to claim 45, wherein said ratio between the atmosphericpressure and the actual intake pressure on the intake valve upstreamside is calculated based on an actual intake air amount sucked into theengine, a throttle full-open time intake air amount sucked into theengine when said throttle valve is fully opened, and a new air rate setaccording to operating conditions of the engine.
 47. A method ofcontrolling an intake air amount of an internal combustion engineaccording to claim 30, wherein an actual intake air amount controlled bythe intake valve is predicted based on the operating characteristic ofthe intake valve and the valve overlap at the operating characteristic,and said target throttle opening is set based on the predicted value andsaid target intake air amount.
 48. A method of controlling an intake airamount of an internal combustion engine according to claim 30, wherein avalve operating area of the intake valve at said target valve operatingcharacteristic is calculated, the valve opening area is corrected basedon a correction value according to the valve overlap, and said targetthrottle opening is set based on the corrected valve opening area andsaid target intake air amount.
 49. A method of controlling an intake airamount of an internal combustion engine according to claim 48, whereinsaid correction value according to the valve overlap is set bycorrecting a basic correction value to be set based on the valve overlapaccording to a valve lift amount.
 50. A method of controlling an intakeair amount of an internal combustion engine according to claim 49,wherein the correction according to said valve lift amount is notperformed when said valve overlap amount is equal to or less than apredetermined amount.
 51. A method of controlling an intake air amountof an internal combustion engine according to claim 48, wherein saidvalve opening area is corrected based on a correction value according tosaid valve overlap, and also according to an engine rotation speed. 52.A method of controlling an intake air amount of an internal combustionengine according to claim 48, wherein the corrected valve opening areais converted into a volume flow ratio, a requested volume flow ratio insaid throttle valve is calculated by dividing a target volume flow ratioequivalent to said target torque by the volume flow ratio, and therequested volume flow ratio is converted to set said target throttleopening.
 53. A method of controlling an intake air amount of an internalcombustion engine according to claim 52, wherein said corrected valveopening area is further corrected based on a flow loss value accordingto said valve lift amount to be converted into the volume flow ratio.54. A method of controlling an intake air amount of an internalcombustion engine according to claim 29, wherein said variable valvemechanism comprises a mechanism varying a valve lift amount of saidintake valve and a mechanism varying valve timing, and a target valvelift amount and target valve timing of said intake valve are set as saidtarget valve operating characteristic.
 55. A method of controlling anintake air amount of an internal combustion engine according to claim54, wherein said mechanism varying said valve lift amount includes: adrive shaft rotating in synchronism with a crankshaft; a drive cam fixedto said drive shaft; a swing cam swinging to operate said intake valveto open and close; a transmission mechanism with one end connected tosaid drive cam side and the other end connected to said swing cam side;a control shaft having a control cam changing the position of saidtransmission mechanism; and an actuator rotating said control shaft, andsuccessively changes the valve lift amount of said intake valve byrotatingly controlling said control shaft by said actuator, and whereinsaid mechanism varying said valve timing successively changes a rotationphase of said drive shaft relative to the crankshaft.